1. Field of the Invention
The present invention relates to an input device which applies an electrically controlled force to a manually operated operating unit, and more specifically relates to a technique for optimizing the time at which the force is applied to the operating unit without being affected by the operating speed of the operating unit.
2. Description of the Related Art
Recently, force-applying bi-wire input devices (hereinafter called “force-applying input devices” in the present specification) in which the operational state of an operating unit is converted into an electrical signal and transmitted to a controlled object and an actuator, such as an electric motor, is controlled so as to apply a suitable force to the operating unit have been proposed and have been used in various applications in place of mechanical input devices in which the operational state of the operating unit is transmitted to the controlled object via a mechanical system. There are several types of force-applying input devices: a slide type and a lever type in which the operating unit can be reciprocated in only one direction, a rotary type in which the operating unit can be rotated around only one axis, a joystick type in which the operating unit can be operated in any direction, etc.
In the case in which the force-applying input device is set such that a predetermined force is applied to the operating unit if the operating unit is at a predetermined position, the time at which the force is applied to the operating unit is controlled as a function of the position of the operating unit. For example, the force-applying input device may be provided with a display which shows one or more symbols and a cursor whose movement is controlled by the operating unit, and a force which pulls the cursor toward the central point of one of the symbols may be applied to the operating unit when the cursor is moved into a region within a predetermined distance from the central point of the symbol. In such a case, the displacement and the moving direction of the operating unit are determined using a position sensor, such as an encoder, and a predetermined actuator drive signal is output from a controller when a position signal output from the position sensor represents a position within a predetermined distance from the central point of the symbol. Accordingly, an external force which pulls the cursor toward the central point of the symbol is applied to the operating unit.
In order to ensure the operational stability of the operating unit, the actuator may be controlled in accordance not only with the position signal output from the position sensor but also with the operating speed of the operating unit which is calculated on the basis of the position signal. In that case, the actuator is controlled such that the resistive force applied to the operating unit increases as the calculated operating speed increases.
However, when the time at which the force is applied to the operating unit is controlled as a function of the position of the operating unit, the controller must first calculate the position of the operating unit on the basis of the position signal output from the position sensor, and then calculate the actuator drive signal corresponding to the calculated position of the operating unit and activate the actuator. Therefore, there is a time lag between when the position and the moving direction of the operating unit are calculated and when the force is actually applied to the operating unit. Accordingly, the force cannot be stably controlled and there is a problem in that the operating unit vibrates at the central point of the symbol when the operating unit is not held by the operator. This problem becomes more severe as the operating speed of the operating unit increases.